System and method for reducing thermal offset in a pressure gauge

ABSTRACT

A pressure measurement device is provided. The pressure measurement device includes a pressure gauge having a hermetically sealed cavity. The cavity is filled with pressure transferring media that includes a first material and a compensator material. The first material has a first coefficient of thermal expansion and the compensator material has a second coefficient of thermal expansion that is lower than the first coefficient of thermal expansion. The pressure measurement device includes a pressure reading mechanism coupled to the pressure gauge and operative to convert a displacement of the pressure gauge to a pressure measurement reading.

BACKGROUND

Technical Field

This application is directed to a pressure gauge and, in particular, aprocess isolated pressure gauge that mitigates thermal offset inpressure measurements.

Description of the Related Art

Conventional sealed pressure gauges are susceptible to thermalvariations. In particular, variations in temperature of a conventionalsealed pressure gauge can introduce a thermal offset in the pressuremeasurements being made by the pressure gauge. The thermal offset is afunction of the temperature change to which the pressure gauge isexposed. Thus, as environmental, or process, temperatures fluctuate, thethermal offset of the pressure gauge also fluctuates. Due to thesethermal offsets, conventional sealed pressure gauges may provideincorrect and flawed pressure measurements.

BRIEF SUMMARY

In an embodiment, a pressure measurement device includes a C-shapedBourdon tube having an interior, a sealed distal end and a proximal endhaving an open inlet. The interior is filled with both a liquid having afirst coefficient of thermal expansion and a compensator material havinga second coefficient of thermal expansion that is lower than the firstcoefficient of thermal expansion. The compensator material occupies agreater amount of a volume of the interior than the liquid occupies.

In an embodiment, the pressure measurement device includes a membranethat covers the open inlet. The membrane has a first surface exposed tothe interior of the C-shaped Bourdon tube and a second surface oppositethe first surface that is exposed to an environment outside of theC-shaped Bourdon tube. In an embodiment, the pressure measurement deviceincludes a pressure reading mechanism coupled to the distal end of theC-shaped Bourdon tube and operative to convert displacement of themembrane, such as the distal end of the membrane, to a pressuremeasurement reading.

In an embodiment, the liquid occupies 10%-30% of the volume of theinterior and the compensator material occupies a remaining volume of theinterior. In another embodiment, the liquid occupies 10%-20% of thevolume of the interior and the compensator material occupies a remainingvolume of the interior. In an embodiment, the compensator material is atleast one of a ceramic, glass, Garolite®, Invar™, plastics and graphite.In an embodiment, the pressure reading mechanism is a mechanicalmechanism or an electronic mechanism. In an embodiment, the liquid isany flowable material and may be a liquid for use in sanitary situationsand is at least one of silicon, mineral oil and water.

In an embodiment, a pressure measurement device includes a pressuregauge having a cavity. The cavity is filled with a pressure transferringmedia including a fluid and a compensator material. The fluid has afirst coefficient of thermal expansion and the compensator material hasa second coefficient of thermal expansion that is lower than the firstcoefficient of thermal expansion. The compensator material is operativeto reduce an overall coefficient of thermal expansion of the pressuretransferring media to be below the first coefficient of thermalexpansion to mitigate a change in a volume of the pressure transferringmedia resulting from a temperature change. In an embodiment, thepressure measurement device includes a pressure reading mechanismcoupled to the pressure gauge and operative to convert a displacement ofthe pressure gauge to a pressure measurement reading.

In an embodiment, the pressure measurement device includes an inlet inthe pressure gauge and a membrane positioned to cover the inlet. In anembodiment, the membrane has a first surface exposed to the cavity and asecond surface opposite the first surface that is exposed to anenvironment outside of the cavity. In an embodiment, the inlet isoperative to convey a pressure of the environment to the pressuretransferring media.

In an embodiment, the pressure gauge is at least one of a C-shapedBourdon tube, a helix, bellows and a diaphragm. In an embodiment, avolume of the compensator material is 70%-90% of the volume of thepressure transferring media and a volume of the fluid is a remainingvolume of the pressure transferring media. In an embodiment, the volumeof the compensator material is 80%-90% of the volume of the pressuretransferring media and the compensator material occupies a remainingvolume of the interior. In an embodiment, the compensator material is atleast one of a ceramic, glass, Garolite®, Invar™, plastics and graphite.In an embodiment, the fluid is at least one of silicon, mineral oil andwater.

In an embodiment, a pressure measurement device includes a pressuregauge having a hermetically sealed cavity. The cavity is filled withpressure transferring media that includes a flowable material and acompensator material. The flowable material has a first coefficient ofthermal expansion and the compensator material has a second coefficientof thermal expansion that is lower than the first coefficient of thermalexpansion. In an embodiment, the pressure measurement device includes apressure reading mechanism coupled to the pressure gauge and operativeto convert a displacement of the pressure gauge to a pressuremeasurement reading.

In an embodiment, the pressure measurement device includes an inlet inthe pressure gauge and a membrane positioned to cover the inlet. Themembrane has a first surface exposed to the cavity and a second surfaceopposite the first surface that is exposed to an environment outside thepressure gauge. The inlet is operative to convey a pressure of theenvironment to the pressure transferring media.

In an embodiment, the pressure gauge is at least one of a C-shapedBourdon tube, a helix, a bellows and a diaphragm. In an embodiment, avolume of the compensator material is 70%-90% of the volume of thepressure transferring media and a volume of the flowable material is aremaining volume of the pressure transferring media. In an embodiment,the volume of the compensator material is 80%-90% of the volume of thepressure transferring media and the compensator material occupies aremaining volume of the interior. In an embodiment, the compensatormaterial is at least one of a ceramic, glass, Garolite®, Invar™,plastics and graphite.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements.The sizes and relative positions of elements in the drawings are notnecessarily drawn to scale.

FIG. 1 is a schematic side view of a pressure measurement device inaccordance with one embodiment.

FIG. 2 is a schematic isometric view of the pressure gauge of FIG. 1coupled to the membrane.

FIG. 3 is a schematic cross-sectional view of the pressure gauge of FIG.2 taken through line A-A.

FIG. 4 is a schematic illustration of a pressure transferring media usedin a pressure measurement device in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of a pressure measurement device 100.The pressure measurement device 100 includes a pressure gauge 102, afill passage 103, a membrane 104, a connector 105, a pressure readingmechanism 106, a pressure indicator 108, a dial plate 110, a mount 112and a housing 114. Although not shown in FIG. 1, the pressuremeasurement device 100 may also include a transparent cover for thepressure indicator 108 and the dial plate 110.

The pressure gauge 102 includes a C-shaped Bourdon tube that has adistal end 116 and a proximal end 118. The distal end 116 is configuredto move relative to the proximal end 118 in response to a change inpressure, as will be explained in more detail below. The pressure gauge102 may be any device that is configured to detect pressure, such as,pneumatic pressure or atmospheric pressure, or a change thereof andconvert the detected pressure or change to a displacement. Although aC-shaped Bourdon tube is shown in FIG. 1, the pressure gauge may beother shapes or types, such as a U-shaped tube, a helix, a spiral,bellows or a diaphragm, among others.

The distal end 116 of the pressure gauge 102 is coupled to the pressurereading mechanism 106. The pressure reading mechanism 106 is, in turn,coupled to the pressure indicator 108. The proximal end 118 of thepressure gauge 102 has an inlet 121 to the fill passage 103 that issealed and covered by the membrane 104. The pressure gauge 102, pressurereading mechanism 106, pressure indicator 108 and dial plate 110 may bepositioned within the housing 114. The membrane 104 may be positionedwithin the connector 105, and the fill passage 103 may be positioned atleast partly within the mount 112. The connector 105 may be used forjoining or fitting the pressure measurement device 100 to another deviceor a process (such as an industrial process).

The pressure reading mechanism 106 detects a displacement of thepressure gauge 102, such as the distal end 116 of the pressure gauge102, and causes the pressure indicator 108 to move. The pressuremeasurement device 100 is calibrated such that a pressure reading thatis indicated on the dial plate 110 by the pressure indicator 108corresponds to the pressure detected by the pressure gauge 102. Althougha mechanical pressure reading mechanism is shown, it will be appreciatedthat the pressure reading mechanism 106 may be an electronic pressurereading mechanism.

FIG. 2 depicts an isometric view of a schematic illustration of thepressure gauge 102 and the membrane 104 of FIG. 1. FIG. 3 is across-sectional view of the pressure gauge 102 taken through line A-A inFIG. 2. As best shown in FIG. 3, the pressure gauge 102 has a hollowinterior 120 that forms a cavity. The interior 120 is hermeticallysealed, or liquid sealed, and isolated from an environment (such as, amanufacturing process) outside of the pressure gauge 102. As used inthis context, liquid sealed refers to a seal that is sufficient toprevent escape of a pressure transferring media 124 disposed withininterior 120 and also prevents contamination of the pressuretransferring media 124 from sources outside the interior 120. As shownin FIG. 2, to enclose the interior 120, the distal end 116 of thepressure gauge 102 is sealed. The proximal end 118, on the other hand,has an inlet 121 to the fill passage 103 that is covered and sealed bythe membrane 104. As used in this context, a fill passage may include astructure formed to allow passage of the pressure transferring media 124into the interior 120 of the C-shaped Bourdon tube. In particular, afirst surface 122 of the membrane 104 interfaces with the interior 120,or more specifically the pressure transferring media 124, of thepressure gauge 102 via inlet 118. A second surface 123 of the membrane104 that is opposite to the first surface 122 is exposed to anenvironment of which pressure is to be measured. The membrane 104 isconfigured to flex in response to pressure being applied to the firstand second surfaces 122, 123. It will be appreciated that, in someembodiments or configurations, the pressure gauge may not include a fillpassage. In such embodiments the membrane 104 may directly interfacewith the interior 120 of the pressure gauge 102. As used in this contextinterfacing can refer to coupling, covering, aligning, connecting,interacting or other suitable interfacing.

The interior 120 of the pressure gauge 102 is filled with the pressuretransferring media 124, which is shown in FIGS. 3 and 4. The pressuretransferring media 124 transfers pressure from the membrane 104 to thepressure gauge 102. The pressure transferring media includes at leasttwo materials, a first material 126 and a second material 128. Thesecond material has a lower coefficient of thermal expansion than thefirst material.

The first material 126 is a flowable material or at least semi-flowablematerial, and in one embodiment is a liquid, such as, for example, wateror mineral oil. In another embodiment, the first material 126 issilicon. It will be appreciated by a person of ordinary skill in the artthat other liquids can be utilized in place of the illustrative liquidsmentioned above. These other liquids are expressly contemplated hereinand the example liquids mentioned herein are merely intended to beillustrative of possible liquids. When placed in the interior 120, thefirst material 126 may freely flow therein and reposition duringdisplacement of the pressure gauge 102.

The second material 128 is a compensator material that, by virtue ofhaving a lower coefficient of thermal expansion than the first material,reduces an overall coefficient of thermal expansion of the pressuretransferring media 124 to be below the first coefficient of thermalexpansion. Advantageously, the second material 128 is a compensationmaterial that is configured to temper, or reduce, the deformation ordisplacement of the pressure gauge 102 in response to changes intemperature. Consequently, more accurate pressure measurement readingsmay be provided. The second material 128 is also referred to herein ascompensator material 128.

The compensator material 128 may any type of material that has a lowercoefficient of thermal expansion than the first material 126, therebydecreasing the overall coefficient of thermal expansion of the pressuretransferring media 124. In some embodiments, the compensator material128 can have a coefficient of thermal expansion that is less than 60% ofthe coefficient of thermal expansion of the first material 126, and insome cases less than 40% of the coefficient of thermal expansion of thefirst material 126. It will be appreciated that the coefficient ofthermal expansion of the compensator material can be selected basedupon, for example, the intended use (e.g., process, environment, etc.)of the pressure gauge 102. The compensator material 128 may include, butis not limited to ceramics, glass, Garolite®, Invar, plastic orgraphite, any other material having a coefficient of thermal expansionthat is less than the first material, or any combination of thesematerials. Additional example compensator materials 128 include diamondor quartz that are associated with a relatively low coefficient ofthermal expansion and are alternatives that may be used. In variousembodiments, the compensator material 128 may be a solid or semi-solidhaving any shape. For example, the compensator material 128 may bebeads, blocks or fibers, among others, that are disposed in the firstmaterial 126. In another embodiment, the compensator material may beflowable or semi-flowable.

As shown in FIG. 3, the compensator material 128 may be stacked in theinterior 120 of the pressure gauge 102 and the first material 126 mayoccupy an annulus on a periphery of the compensator material 128. InFIG. 4, where a suspended pressure transferring media 124 is shown, thecompensator material 128 may be beads that are dispersed within thefirst material 126.

The overall coefficient of thermal expansion of the pressuretransferring media 124 may be a weighted average of the first and secondmaterials. In the weighted average, the first coefficient of thermalexpansion is weighted or scaled by a proportion of a volume of the firstmaterial 126 to an overall volume of the pressure transferring media124. The second coefficient of thermal expansion is weighted or scaledby a proportion of a volume of the second material 128 to an overallvolume of the pressure transferring media 124.

In operation, pressure of the environment is transferred from themembrane 104 to the pressure gauge 102. When the pressure measurementdevice 100 is exposed to an environment of increased pressure, themembrane 104 flexes toward the interior 120 of the pressure gauge 102,thereby applying pressure to the pressure transferring media 124 therebycausing the pressure gauge 102 to deform and experience a displacement.That is, the distal end 116 of the pressure gauge 102 is displaced(e.g., uncoiled). The pressure reading mechanism 106 detects thedisplacement of the pressure gauge 102 and converts the displacement toa pressure measurement as described with reference to FIG. 1. When thepressure at the membrane 104 is relieved, the tube will be induced toretreat to its original form.

Conversely, as the pressure measurement device 100 is exposed to anenvironment of decreased pressure, the membrane 104 flexes away from theinterior 120 of the pressure gauge 102, thereby releasing pressure onthe pressure transferring media 124. In response to the release of thepressure transferring media 124, the distal end 116 of the pressuregauge 102 is displaced (e.g., coiled). Again, the pressure readingmechanism 106 detects the displacement of the pressure gauge 102 andconverts the displacement to a pressure measurement.

Similarly, when the pressure gauge 102 is a helix (or a spiral), theapplication of pressure will induce the helix to unwind. The unwindingor displacement resulting from the unwinding is converted to thepressure measurement. In addition, when the pressure gauge 102 is abellows, the application of pressure will induce the bellows to expand,resulting in a displacement that is convertible to a pressuremeasurement. These are merely meant to be illustrative of possiblepressure gauges and should not be viewed as limiting of this disclosure.

Advantageously, including the compensator material 128 in the pressuretransferring media 124 reduces the propensity of the pressuretransferring media 124 to change in volume or expand in response totemperature changes to which the pressure measurement device is exposed.It is to be appreciated that the reduction is proportional to the volumeof the compensator material 128 within the pressure transferring media124 and the interior 120 of the pressure gauge 102.

In embodiments, the second material 128 consumes more of the volume inthe pressure gauge 102 than the first material 126. In one embodiment,the compensator material 128 is between 70%-90% of the volume of thepressure transferring media 124. The volume of the first material 126may be the remainder of the volume of the pressure transferring media124 not occupied by the compensator material 128. Accordingly, in theembodiment in which the compensator material 128 is a solid, the firstmaterial 126 is significant enough in volume to freely flow andreposition within the interior 120 such that the pressure transferringmedia 124 does not impede the displacement of the gauge 102. In anotherembodiment, the volume of the compensator material 128 may also be80%-90% of the volume of the pressure transferring media 124. The volumeof the first material 126 may be the remaining 10%-20% of the volume ofthe pressure transferring media 124 not occupied by the compensatormaterial 128.

In an embodiment, the compensator material 128 may advantageously have alower mass than the first material 126. In that regard, the compensatormaterial 128 may improve the shock resistance of the pressure gauge 102.Furthermore, when a material of lower mass is used, the likelihood ofbending or deforming the gauge 102, for example, due to a gravitationalforce, is also reduced.

The first material 126 (and the compensator material 128) mayadvantageously be materials used in sanitary situations or sterileenvironments. In the event of a breach of the membrane 104 or thepressure gauge 102, the pressure transferring media 124 may escape thepressure gauge 102 to the environment outside of the pressure gauge 102(whose pressure is sensed or monitored using the pressure measurementdevice 100). The environment may be an industrial or a manufacturingfacility (such as a food production facility or an industrial paintproduction facility, among many others). The release of any unsanitarymaterial may compromise the facility, conflict with established hygienicor manufacturing standards, and require significant remediation.However, the release of sanitary or sterile material may be enduredwithout significant remediation.

Reducing the coefficient of thermal expansion of the pressuretransferring media (or the propensity of the volume of the pressuretransferring media to change in relation to temperature) improves thepressure sensing ability of the gauge 102 and the pressure measurementdevice 100. Further, reducing the coefficient of thermal expansion ofthe pressure transferring media decouples pressure measurement from theeffects of temperature variation. The impact of temperature on pressuremeasurement is reduced. The resulting pressure measurement is moreaccurate, as it is less susceptible to temperature changes.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

What is claimed is:
 1. A pressure measurement device comprising: aC-shaped Bourdon tube having an interior, a sealed distal end and aproximal end having an open inlet, the interior being filled with aliquid having a first coefficient of thermal expansion and a compensatormaterial having a second coefficient of thermal expansion that is lowerthan the first coefficient of thermal expansion, the compensatormaterial occupying a greater amount of a volume of the interior than theliquid occupies; a membrane positioned to cover the open inlet, themembrane having a first surface that interfaces with the interior of theC-shaped Bourdon tube and a second surface opposite the first surfacethat is exposed to an environment outside of the C-shaped Bourdon tube;and a pressure reading mechanism coupled to the distal end of theC-shaped Bourdon tube and operative to convert displacement of thedistal end to a pressure measurement reading.
 2. The pressuremeasurement device of claim 1, wherein the liquid occupies 10%-30% ofthe volume of the interior and the compensator material occupies aremaining volume of the interior.
 3. The pressure measurement device ofclaim 2, wherein the liquid occupies 10%-20% of the volume of theinterior.
 4. The pressure measurement device of claim 1, wherein thecompensator material is at least one of a ceramic, glass, Garolite®,Invar™, plastics and graphite.
 5. The pressure measurement device ofclaim 1, wherein the pressure reading mechanism is a mechanicalmechanism or an electronic mechanism.
 6. The pressure measurement deviceof claim 1, wherein the liquid is a sanitary liquid and is at least oneof silicon, mineral oil and water.
 7. A pressure measurement devicecomprising: a pressure gauge having a cavity, the cavity being filledwith a pressure transferring media including a fluid and a compensatormaterial, the fluid having a first coefficient of thermal expansion andthe compensator material having a second coefficient of thermalexpansion that is lower than the first coefficient of thermal expansion,the compensator material being operative to reduce an overallcoefficient of thermal expansion of the pressure transferring media tobe below the first coefficient of thermal expansion to mitigate a changein a volume of the pressure transferring media resulting from atemperature change; and a pressure reading mechanism coupled to thepressure gauge and operative to convert a displacement of the pressuregauge to a pressure measurement reading.
 8. The pressure measurementdevice of claim 7, comprising: an inlet in the pressure gauge; and amembrane positioned to cover the inlet, the membrane having a firstsurface that interfaces with the cavity and a second surface oppositethe first surface that is exposed to an environment outside of thecavity, the inlet being operative to convey a pressure of theenvironment to the pressure transferring media.
 9. The pressuremeasurement device of claim 7, wherein the pressure gauge is at leastone of a C-shaped Bourdon tube, a helix, bellows and a diaphragm. 10.The pressure measurement device of claim 7, wherein a volume of thecompensator material is 70%-90% of the volume of the pressuretransferring media and a volume of the fluid is a remaining volume ofthe pressure transferring media.
 11. The pressure measurement device ofclaim 10, wherein the volume of the compensator material is 80%-90% ofthe volume of the pressure transferring media.
 12. The pressuremeasurement device of claim 7, wherein the compensator material is atleast one of a ceramic, glass, Garolite®, Invar™, plastics and graphite.13. The pressure measurement device of claim 7, wherein the fluid is atleast one of silicon, mineral oil and water.
 14. A pressure measurementdevice comprising: a pressure gauge having a sealed cavity, the cavitybeing filled with pressure transferring media that includes a flowablematerial and a compensator material, the flowable material having afirst coefficient of thermal expansion and the compensator materialhaving a second coefficient of thermal expansion that is lower than thefirst coefficient of thermal expansion; and a pressure reading mechanismcoupled to the pressure gauge and operative to convert a displacement ofthe pressure gauge to a pressure measurement reading.
 15. The pressuremeasurement device of claim 14, comprising: an inlet in the pressuregauge; and a membrane positioned to cover the inlet, the membrane havinga first surface exposed to the cavity and a second surface opposite thefirst surface that is exposed to an environment outside the pressuregauge, the inlet being operative to convey a pressure of the environmentto the pressure transferring media.
 16. The pressure measurement deviceof claim 14, wherein the pressure gauge is at least one of a C-shapedBourdon tube, a helix, a bellows and a diaphragm.
 17. The pressuremeasurement device of claim 14, wherein a volume of the compensatormaterial is 70%-90% of the volume of the pressure transferring media anda volume of the flowable material is a remaining volume of the pressuretransferring media.
 18. The pressure measurement device of claim 17,wherein the volume of the compensator material is 80%-90% of the volumeof the pressure transferring media.
 19. The pressure measurement deviceof claim 14, wherein the compensator material is at least one of aceramic, glass, Garolite®, Invar™, plastics and graphite.
 20. Thepressure measurement device of claim 14, wherein the cavity ishermetically sealed, or liquid sealed, and isolated from an environmentoutside of the pressure gauge.